1. Field of the Invention
This invention relates to a touch panel, more particularly, to a touch panel in which the contact conductive layer is substituted with phototransparent organic conductive films to give conductivity per se, thus not requiring the coating process of the conductive layer and resolving problems of crack bacause of the conductive layer.
2. Description of the Related Art
A touch input system, including a touch panel which determines the position of an object which is in contact with a contact surface, has been used variously in the fields of computer graphics, and design and manufacturing systems using computers. The touch system denotes a system consisting of a digitizer which responds to a touch on a specific position of a contact surface, and can be driven by touching with the finger of an operator because of a transparent covering layer on a conductive surface.
The driving principle of a touch panel in the touch panel system is as follows:
A contact surface of a touch panel has equal specific electrical resistance and is connected to an electrode made of a material of which conductivity is greater than that of the contact surface. This touch input system consists of a means which applies an electrical potential across a contact surface in the direction 2 or the direction vertical to the direction 1 after an electrical potential across a contact surface in the direction 1 is applied. Consequently, if the contact is touched by the finger of an operator or an object such as a touch pen, an electrical potential of the touched position is measured which corresponds to a distance between positions of objects on contact surface as well as the distance between an electrode and an object. The system consists of means not only providing x-y coordinates but also determining and providing z axis value on the basis of parameters of pressure or position. Dot space plays the role of wrapper for double film and dot space tip in the dot spaces damages conductive layer (2') easily by being applied on the conductive layer (2') heavily to induce crack of the conductive layer, which is caused by the formation of the wrapper and the sharpness of a tip. Therefore, by blunting the formation of the wrapper and the sharpness of the tip using adhesive as a cushion, some problems of crack are solved, but there still remain problems that the blunt space tip is difficult to make and there are no essential countermeasures for crack on the conductive layer. To solve the problems, the structure of the touch panel double film in FIGS. 1 and 2 is used. The structure consists of the conductive layers formed on the upper part of the base substrate and on the lower part of the double film which are separated by insulated dot space (3), and the lower film coated with the upper film (5') on both sides thereof, and the hardcoating layer thereon.
The touch panel with this structure is operated according to a principle that coordinate values are recognized using positional change of resistance values when substrate conductive layer (2) of the base substrate and contact conductive layer (2') of the film are attached by touching with a touch pen. In general, glass, plastics or various printer circuit substrate materials, or a rigid body such as a metal with an insulated layer are used as the base substrate (1), and a hard plate coated with plastic material in the form of a soft layer thereon, as well.
Conductive layers (2, 2') consist of a transparent conductive material for which typically indium tin oxide (ITO) is used. Polyester group resins such as polyethylene terephtalate (PET) and polycarbonate are used as the films (5, 5').
FIG. 1 indicates the structure with conductive layers coated on both sides of the lower film (5) and FIG. 2 indicates the structure in which only the substrate conductive layer (2) of the upper part of the base substrate and the conductive layer attached thereto are used by coating only one side of the lower film (5).
Generally, the film of a thickness of about 25 .mu.m is used as the lower film, and the thickness of the conductive layer can be adjusted to about 100 .ANG. as a conductive layer having the resistance of 300 .OMEGA./.quadrature. is used.
The crack is solved to some degree using the double film structure in FIGS. 1 and 2. However, problems still remain because the crack of the conductive layer is eventually generated which causes an error in operation by changing the value of resistance, and particular countermeasures therefor have not been developed so far.